334 Mr. R. Hope on two neio 



of Bowerbank's genus Microciona^ taken in a strict sense, 

 that is to say, of that section of the genus which agrees with 

 the type, M. atrosanguinea, in the possession of monactinal 

 megasclera of three kinds, with " navicular " isochelse and 

 toxites as microsclera. It is in this stricter sense alone that 

 the generic term Microciona is used throughout this paper. 

 In all other respects the classification followed is that of 

 Messrs. Hidley and Dendy, to whose diagnoses of the genera 

 &c. in their Report on the ' Challenger ' Monaxonida 1 refer. 

 I propose for this sponge the specific name of strepsitoxa 

 (Gr. cTTpe^ft), I twist) , from a peculiarity of the toxa referred 

 to below. 



Microciona strepsitoxa^ n. sp. 



The sponge coats about four square inches of the flat valve 

 of a scallop-sliell [Pecten^ sp.), attaining in the furrows of the 

 shell a maximum thickness of about 1 millim. Its colour, 

 when fresh, was scarlet, but in spirit it rapidly and completely 

 faded to a dead white. Surface, when fresh, smooth ; in the 

 dry state hispid, from the projecting ends of the spicular 

 brushes of the skeleton. The oscula are numerous and run 

 deep into the sponge ; the pores small and generally distri- 

 buted over the surface. 



The skeletal columns, as usual in the genus, rise vertically 

 from the base to the surface ; they are slender at the base 

 and rarely branched, and they end in thick brushes of 

 spicules which, spreading out obliquely in contact with each 

 other, are traversed horizontally by sheaves of long slender 

 styles imbedded in the sponge-substance. As usual also in 

 Microciona, the main skeletal spicules increase in length 

 towards the surface of the sponge, the shortest, as a rule, 

 forming the base of the columns. 



Spiculation. — Megasclera, three : — 



1. Styles, sometimes straight, but generally slightly curved, 

 constricted about one diameter above the base, sometimes 

 smooth, but usually basally spined or tuberculated. They 

 vary greatly in length, ranging from '480 to "636 millim., 

 with a few much shorter ; breadth '0105 to "012 millim. 

 (figs. A, 1 and 2). 



2. Straight or slightly curved, tapering, entirely spined styles 

 and tylostyles, varying in length from about '1 to "2 millim. ; 

 average breadth about '006 millim. (fig. A, 3). 



3. Long, smooth, slender, subclavate styles, from about '25 

 to '31 millim. long by about "004 millim. broad. With a 

 high power the heads frequently appear slightly roughened 

 (%A,4). 



